There is continual need to improve response time and resolution in controlling the movement of devices where a controller and feedback loop are incorporated. In these situations, controllers are interfaced with devices and combinations of sensors and device drivers to compose an overall feedback loop. A controller initiates a certain action on a device through the driver circuit, a sensor circuit acquires information regarding how the device has responded to the drive input, and a modified new drive input is calculated. This type of control loop is widely pursued in brushless DC motor (BLDC) commutation and in systems incorporating fans being driven by these motors.
Hall effect sensors are part of a technology application incorporating a magnet on the device being controlled. The Hall effect sensor is used to detect the proximity of a magnetic field coming from the magnet and therefore providing information about a location and movement of the device the magnet is attached to. For example, controlling the speed of a fan connected as part of a DC brushless motor is highly desirable. Maintaining a speed relative to a temperature sensed in the fan's environment and adjusting the speed for maintaining a constant temperature is a technique frequently used.
With reference to FIG. 1, a type of Hall effect sensor, known as a Hall device 125, is powered by connections to a supply voltage VDD 110 and ground 112 within a device controller system 100. The Hall device 125 incorporates additional devices and circuitry beyond an elemental Hall sensor to provide current and voltage sensing capability in a single component. A controller 105 is connected to power between supply voltage VDD 110 and ground 112. The controller 105 conducts the general processes of the system. The Hall device 125 has a Hall device output pin 150 connecting to a controller input pin 135.
Each of two output pins 140a and 140b of the controller 105 connects to a control input of a device driver 120a and 120b. Each of two device drivers 120a and 120b contains a drive resistor 122a and 122b and a drive transistor 124a and 124b. Each of two drive resistors 122a and 122b connects between an input of a device driver 120a and 120b and a base terminal of the corresponding drive transistor 124a and 124b. Each emitter terminal of the drive transistors 124a and 124b connects to ground 112. Each of two fan coils 130a and 130b connects between a fan power supply 115 and a collector terminal of a respective drive transistor 124a and 124b. Each fan coil 130a and 130b relates to one phase of a brushless DC (BLDC) motor (not shown).
The brushless DC motor has magnetic poles associated with a rotor (not shown). During rotation, the magnetic poles of the rotor pass by the Hall device 125, each creating a Hall voltage pulse on the Hall device output pin 150. For a two-phase motor, two pulses will be produced on the Hall device output pin 150 for each rotation of the motor. The Hall voltage pulse is used as input to the controller 105 as part of a commutation scheme for the motor. During the first portion of the brushless DC motor commutation cycle, the Hall voltage pulse is coupled to the controller 105 through the controller input pin 135. The Hall voltage pulse switches between 0 V (volts) and VDD 110 in response to variations of the associated fields from the magnetic rotor poles. The toggling of the Hall voltage pulse is used in combination with programming within the controller 105 as part of the commutation scheme to control the speed of the fan.
The commutation scheme uses a change in the Hall voltage pulse to trigger an interrupt programming routine operating within the controller 105. The interrupt routine interrogates a timer that has been counting up since a last change in the Hall voltage pulse. According to how much time has elapsed since the last change in Hall voltage pulse, and taking into account the rising or falling transition of the present change in the Hall voltage pulse, the controller 105 will produce fan coil control signals at the port pins 140a and 140b. The fan coil control signals are coupled to the device drivers 120a and 120b where they produce a base voltage at the base terminal of the driver transistors 124a and 124a. Changes in the base voltage on the driver transistors 124a and 124b vary the amount of current conducted through the fan coils 130a and 130b. The varying current, in turn, modulates the magnetic field in the coils controlling the respective phases of the brushless DC motor. By varying the timing and duration of the fan coil control signals, the controller 105 will maintain or change the fan speed according to requirements of the programming.
Presently, the use of a Hall device 125 means that in addition to an elemental Hall sensor, devices and circuitry are incorporated in the device to provide current and voltage sensing capability in a single component. The additional circuitry causes the Hall device 125 to cost significantly more than the elemental Hall sensor. Additionally, the controller 105 contains additional components and circuitry capable of measuring signals and voltages. Presently, not all of the measuring components in the device controller system 100 are incorporated in the measurement process. A typical device controller system 100, therefore, may contain components with costly additional measurement circuitry, while at the same time, the system may have measurement components available that are going unused. It would be desirable for a device controller system 100 to be able to use a less expensive Hall sensor and at the same time incorporate any components already available within the system to measure the Hall voltages produced and provide a more cost-effective commutation scheme.